The css3-transitions spec should answer the question of which
changes to the transition-* properties affect transitions that have
already started.
It seems highly impractical to start transitions for changes that
have already completed if the transition properties change such that
they would still be transition had the transition properties been
set that way when the change originally occurred.
This suggests that it might be best to ignore all dynamic changes to
transition-duration and transition-delay (and probably
transition-timing-function, although that's not as much of an
issue).
And it seems entirely reasonable, and probably most visually
desirable, to run transitions to completion on the same animation
function and timing that they started with.
However, authors sometimes want to stop currently running
transitions. I think the solution here that imposes the least
inconsistency is the spec saying that running transitions should
stop if the 'transition-property' value changes such that the
property/element pair would no longer transition. This appears to
be what WebKit does, and is what I plan to implement in Mozilla.
-David
--
L. David Baron http://dbaron.org/
Mozilla Corporation http://www.mozilla.com/